1. Lagos, Nigeria (1/12)

The booming political, financial and commercial capital of Nigeria is a port city that in recent years has become a major oil exporter. It is a magnet for the country’s growing population, which is increasing by about 4.3 million people a year, according to United Nations’ estimates—an annual increase of about 2.5 percent. The majority of Nigerians still live in the countryside so there is a lot of potential for further urbanization as the country’s economy develops and rural-urban migration continues. (Source: Reuters)

2. Dhaka, Bangladesh (2/12)

One of the most densely populated cities in the world, there is sometimes very little room to do business in the commercial capital of Bangladesh. The city has always attracted rural migrants and now increased foreign investment, commerce, and growing service and textile industries have accelerated the trend. Located on the lower reaches of the Ganges delta, the city is built on flat land close to sea level and is therefore vulnerable to flooding during the monsoon season and due to heavy rains during tropical cyclones. (Source: Reuters)

3. Shenzhen, China (3/12)

Visitors stand in front of a portrait of the late Chinese leader Deng Xiaoping in Shenzhen. Located on the southern coast of China, Shenzhen was only a small village in 1970. However, four decades of double-digit growth (between 1990 and 2011 it grew by nearly 12 percent every year) and its status as China’s first Special Economic Zone has turned the city into a powerhouse of China’s manufacturing boom and one of China’s busiest container ports. (Source: Reuters)

4. Karachi, Pakistan (4/12)

Students attend a rooftop evening class in a private school in a slum area in Karachi, the largest city, main seaport and financial center of Pakistan. Karachi is the second largest city proper in the world after Shanghai and accounts for about 20 percent of Pakistan’s GDP. It was the capital city until Islamabad was created to spread development more widely across the country. It is growing rapidly due to rural-urban migration and has recently seen expansion of IT, software, outsourcing and communications industries. (Source: Reuters)

5. Delhi, India (5/12)

The capital of India has in recent times grown faster than its more exalted and glamorous rival Mumbai, which it recently overtook to become India’s largest city. Delhi’s rapid growth reflects its position as political capital of the country, tourism center, and a hub for service industries, as well as comparatively rapid population growth in the neighboring states of northern India such as Uttar Pradesh. Rural-urban migration from these states, whose agricultural resources are struggling to support expanding populations, has been a major factor. (Source: Reuters)

6. Beijing, China (6/12)

As China’s economy continues to grow and to develop sectors aside from manufacturing and heavy industry, Beijing is likely to thrive as the center for government, finance, retail and other tertiary industries. One result has been its now notorious traffic jams and air pollution. One in four residents of Beijing is a migrant from the countryside and that pattern will likely continue as China’s rate of urbanization remains low compared with advanced industrialized nations. (Source: Reuters)

7. Guangzhou, China (7/12)

Migrant workers chat at their temporary house near a construction site in Guangzhou. Historically known as Canton, Guangzhou is China’s third largest city and located on the Pearl River in southern China northwest of Hong Kong. It is a critical trading port and capital of China’s industrial and manufacturing province of Guangdong, which has been one of the fastest urbanizing areas of the world for many years. (Source: Reuters)

8. Shanghai, China (8/12)

A bolt of lightning strikes the Oriental Pearl Tower as others light up the skyline above the Pudong financial district in Shanghai, the most recognizable symbol of China’s recent economic ascent and its transformation from a rural to an urbanized nation. In 1980, less than a fifth of China’s population lived in cities. Today, Chinese urbanites number twice the total U.S. population, thanks to one of the largest internal migrations in human history, and Shanghai is ranked as the planet's largest city proper. Despite an aging population, an excess in births over deaths will help keep population growth going, according to the UN. (Source: Reuters)

9. Manila, Philippines (9/12)

An e-jeepney, an electric-powered version of the country's most recognizable icon and favoured form of public transport, goes for a test drive in Manila. The e-jeepney made its debut in the city's streets in an effort to help control urban pollution and climate change. As the Philippines emerges to become one of the next generation of Asian economic powerhouses, the capital Manila is set to continue its spectacular growth, although it faces huge challenges posed by the more than 3 million people living in slums without electricity, sanitation, and access to drinking water. (Source: Reuters)

10. Mumbai, India (10/12)

Western India’s commercial and financial capital, and for centuries a trading gateway to the West, the port of Mumbai continues to attract migrants from the rural hinterlands of central India and beyond, not least those attracted by the lure of Bollywood. With high birth rates and the continued influx of migrants, Mumbai’s population is expected to grow rapidly in the future, although over half of the city’s population lives in slums. (Source: Reuters)

11. Istanbul, Turkey (11/12)

Worshippers attend their first Friday prayer for the holy month of Ramadan at Sultanahmet mosque, known as the Blue mosque, in Istanbul. Standing on the banks of the Bosphorus at a historic crossroads between Europe and Asia, Istanbul has grown in recent years thanks to a young and expanding population (about 1 percent a year) and a rapidly growing economy. If Turkey joins the European Union, Istanbul would become by far Europe’s largest city. (Source: Reuters)

12. Cairo, Egypt (12/12)

The crescent moon is seen near mosques in old Cairo. The largest urban area in Africa and in the Arab world vies with Lagos to be considered the most significant city on the African continent and, as in Nigeria, Egypt’s young and growing population (about 1.4 million people added every year) will continue to feed its principal political, commercial and cultural capital. Moreover, Egypt is still a rural country with 57 percent of people living in the countryside. The potential capacity for further rural-urban migration is enormous. (Source: Reuters)

Top ten largest cities exposed to natural disasters

Buenos Aires (1/10)

Population: 13.5 million. Risks: Droughts, floods. Lightning streaks across the sky in Buenos Aires during a thunderstorm in April 2010. In 2012, Argentina was struck with severe drought, which reduced crop harvests by 10 million tons. Over the summer, Buenos Aires baked in temperatures over 40 degrees Celsius and with 80% less rain than usual. Ironically, in September and November the area then suffered from flooding due to heavy rains which further damaged farming prospects in a nation that is one the world’s top exporters of soy. (Source: Reuters)

Karachi (2/10)

Population: 13.9 million. Risks: Cyclones, droughts, floods.
Pakistani students carry placards requesting relief for children in earthquake-affected area during a rally in Karachi in 2005. Karachi has also suffered from heavy rains and incidents of flooding over the last 20 years, with the effects exacerbated by swift population growth, crushing poverty and government corruption. The risk of flooding has also risen with the melting of nearby glaciers, which in turn has been hastened by pollution from major cities near the Himalayas like Karachi. (Source: Reuters)

Kolkata (Calcutta) (3/10)

Population: 14.4 million. Risks: Cyclones, droughts, floods.
Calcutta residents attempt to remove a tree which was uprooted during a severe cyclonic storm with heavy rains in the eastern Indian city of Calcutta in 2009. Cyclone Aila resulted in over 150 deaths in India, with hundreds more missing and hundreds of thousands homeless. At the 2007 U.N. climate conference in Bali, Calcutta was named the most vulnerable city in the world with respect to climate change, as a result of factors such as its high population density, large slum areas, high pollution and frequent incidence of monsoons. (Source: Reuters)

Dhaka (4/10)

Population: 15.4 million. Risks: Cyclones, droughts, floods.
An Islamic leader distributes relief to a flood victim at Matuail near Dhaka, Bangladesh, in August 2007 when more than half of the low-lying, densely populated nation of 140 million people was covered by flood waters. Bangladesh will need $10 billion from big polluting nations to help it adapt to the effects of climate change, chief of the parliamentary standing committee on environment and forests has said. As one of the world's most densely populated and poorest countries, Bangladesh is highly vulnerable to cyclones, droughts and floods, which often affect millions of people. (Source: Reuters)

São Paulo (5/10)

Population: 19.9 million. Risks: Floods.
Garbage floats on the Pinheiros River, one of São Paulo's biggest, in the wake of flash-flooding that left seven dead in South America's largest city in 1999. The city was in a state of emergency for several days, with rescuers digging through rubble in slum areas where villagers were missing after the destruction from heavy rains. In 2011, over 600 people were killed by flooding and landslides, including dozens in the São Paulo area. While Brazil has been cheered by strong economic growth in recent years, it is also dogged by claims of governmental incompetence and lack of sufficient disaster planning. (Source: Reuters)

Shanghai (6/10)

Population: 20.2 million. Risks: Cyclones, floods.
A pedestrian in a raincoat squats at the Bund near the Huangpu River amid strong winds and heavy rainfall as Typhoon Haikui hit Shanghai, August 8, 2012. The typhoon packed winds of up to 110 km per hour (68 mph), prompting officials to evacuate nearly 2 million people and grounding hundreds of flights to and from Shanghai and other cities. It was also reported in August that Shanghai is the world’s most flood vulnerable city, due to its coastal location and a variety of social and economic factors, including the number of elderly living in proximity to water. (Source: Reuters)

New York-Newark (7/10)

Population: 20.4 million. Risks: Hurricanes, cyclones, floods.
A U.S. flag flies over the foundation of a home destroyed by the storm surge of superstorm Sandy in the Staten Island borough neighborhood of Oakwood in New York, November 28, 2012. The metropolitan New York area was severely shaken by Hurricane Sandy, a grim reminder of the area’s high vulnerability to storms and flooding. While the city has relatively good infrastructure and disaster planning, it’s coastal location and high population density leaves millions starkly exposed to disasters, as well as to the effects of global warming in the form of rising sea levels. (Source: Reuters)

Mexico City (8/10)

Population: 20.4 million. Risks: Droughts, floods, landslides.
Mexican rescue workers light candles during an earthquake anniversary mass in Solidaridad Plaza in Mexico City, September 2005. The devastating aftermath of Hurricane Katrina stirred up memories of the 1985 8.1 earthquake that lasted less than 60 seconds, but reduced parts of Mexico City to rubble and killed thousands. More recently, the city has suffered from deadly landslides, the result of heavy rain combined with poor building construction – like many megacities, Mexico City is home to millions of urban poor who live in “shantytown” housing that is at high risk of disaster. (Source: Reuters)

New Delhi (9/10)

Population: 22.7 million. Risks: Earthquakes, droughts, floods.
A cyclist makes his way through water on a flooded street after heavy rains in New Delhi. The Indian capital has experienced exceptional population growth – as much as 55% from 1991 to 2011. The rapid and haphazard growth has put immense pressure on the city’s infrastructure, which contains many structurally unsound buildings and structures which are highly vulnerable to fire and floodwaters. In addition to high population density and poor infrastructure, Delhi’s location in an active seismic zone puts the fragile balance of the city at great risk. (Source: Reuters)

Tokyo (10/10)

Population: 37.2 million. Risks: Cyclones, earthquakes, floods.
Lights are turned off to save energy before rolling blackouts in Tokyo, March 2011, after an earthquake and tsunami hit northern Japan. Tokyo Electric Power Co announced the blackouts after its power generation was cut due to damage to the Fukushima Daiichi power plant. While the city mostly escaped any major effects the March 2011 earthquake, scientists fear that another similarly powerful quake within Tokyo is likely, and could be devastating. While the city is well-prepared for natural disasters, its demographics pose a challenge – nearly one-fifth of the city’s residents are over 65; with so many elderly people, evacuations could be difficult. (Source: Reuters)